1. Field of the Invention
The present invention relates generally to a roadway worker warning system and method, and more particularly, to a train detection and warning system for train operators and roadway workers working in proximity to railroad tracks.
2. Description of Related Art
Roadway workers are always at risk of accidents if they are not sufficiently warned of approaching trains while working on and around railroad tracks. Because of the noise and commotion of construction and repair activities, workers working in the proximity of railroad tracks need to be alerted of approaching trains that they might otherwise not see or hear.
Several methods and systems are known in the prior art that attempt to provide adequate warning of approaching trains. For example, it is common for flaggers to be positioned at a specific distance from the work area so that they can warn the roadway workers of an approaching train using flags and whistles. However, loud noises generated from work activities can distract the workers making them unable to recognize visual and audible warnings provided by the flagger, the construction noise and activity can even distract the flaggers themselves, thus rendering this method unreliable for providing adequate warning and ensuring the workers' safety.
Many systems have been developed in the past to attempt to improve roadway worker's safety by detecting an approaching train and warning the roadway workers before the arrival of the train at the work site. One such system is disclosed in U.S. Pat. No. 3,167,282 which discloses the use of depression detectors connected to the rail, the detectors operable to sense a deflection in the track indicating an approaching train. The detection of a train triggers a radio signal that transmits a warning signal. However, the depression detectors are mechanical components which are mounted on the rail and require a significant amount of setup effort in order to deploy such sensors on the track. Moreover, depression detectors are the only train detection source used by this system and hence failure of the depression detector results in failure of the complete system.
Another solution is proposed in U.S. Pat. No. 7,624,952 which discloses the use of a transceiver placed on board the train, the transceiver transmitting signals continuously. The signals from the transceiver are received by personal pocket devices carried by the workers, the personal pocket devices sound an alarm upon receiving the warning signal to alert the roadway workers of the approaching train. One obvious drawback of this detection method is that a transmitting apparatus needs to be placed on board every train, without which detection and communication with the personal pocket devices is not possible. Furthermore, this approach is based on direct communication between the train transceiver and the personal pocket devices worn by the workers—which means that any radio interference can result in failure of the system.
Another solution is proposed in U.S. Pat. No. 7,624,952, for use with trains equipped with vehicle on board controls (VOBC), which can control the emergency brakes, cab displays and other on-board devices, such as tag readers. This solution suggests the placement of non-portable tags which are interfaced with nearby train signals. A tag reader placed on board the train reads the tag, the vehicle on board controls (VOBC) then warns the train operator through a cab display. A prerequisite of this detection method is that the non-portable tags need to be interfaced with the electrical train signals in order to sense the current status of the signal. However, while the portable tags can be easily placed near the tracks, the system does not address system security and the potential misplacement of the portable tags. Moreover, this system requires a separate setup on every locomotive which can read tags placed alongside the rail. This means that the detection system requires time, effort, and compliance by other parties before it can be reliably used.
Another suggested solution is the use of a portable train detector unit as disclosed in U.S. Pat. Nos. 8,109,474 and 7,624,952. The train detector unit uses dual ultrasonic sensors and is positioned adjacent to the rail in order to detect the movement of a train wheel. A primary drawback of this system is that ultrasonic sensors have a very low sensing range—about 20 inches —and thus the detection unit needs to be mounted on the rail in order to detect the train wheels. Furthermore, the mounting for the detection unit needs to be adjusted under the rail with specialized clamping means. This may prove to be dangerous if the mounting is not properly adjusted under the rail or the clamping means are not fastened enough, causing damage to the detection unit upon the passage of a train, rendering the system inoperable and leaving the roadway workers unaware of the incoming train.
Yet another approach has been described in U.S. Pat. No. 6,113,037, based on the deployment of magnetometer sensors probes near the railroad track to be monitored. On detection of a train the sensor probes send detection signals to a receiver unit through an RF transmission means. The receiver unit, upon receiving the detection signal, alerts the roadway workers through a crew warning device. One drawback of this system is that the sensitivity of the sensor probes needs to be adjusted so that a warning is generated only upon the passage of a train and not when heavy construction equipment or vehicles pass by, otherwise those vehicles may trigger false alarms. Furthermore, the probes are connected to the sensing units via wires, thus any connectivity issue with the electrical equipment may cause the sensing units to be ineffective. Furthermore, the setup of the train detection and warning equipment in a system of this type is difficult and labor intensive as it requires installation of electrical equipment and wiring arrangements for the hardware.
Another system is disclosed in U.S. Pat. No. 7,538,666, an accountability system used to provide information—such as the presence and location of personnel and objects. The system uses passive, infrared-based, low power RF transmitters and receivers in the form of locator transponders and personal transceiver devices. The personal transceiver device receives an RF signal transmitted by a locator transponder if an object is detected. The received RF signal is then retransmitted by the personal transceiver device to a command base monitor which is used to track a person moving through a building or area and monitor other working parameters of the person. Although this system can be used to detect an incoming train and warn the roadway workers, it relies on the use of a single sensor based on passive infrared radiation, for detecting trains which makes it vulnerable to false alarms under certain environmental conditions. Furthermore, the RF communication link between the locator transponder and the personal transceiver device is not redundant and radio interference can result in communication link failure and the failure of the entire system.
Thus, it can be seen that there remains a need in the art for a system to detect and warn roadway workers of approaching trains in a reliable and efficient manner.